The extensive data storage needs of modern computer systems require large capacity mass data storage devices. A common storage device is the rotating magnetic disk drive.
A disk drive typically contains one or more smooth, flat disks which are rigidly attached to a common spindle. The disks are stacked on the spindle parallel to each other and spaced apart so that they do not touch. The disks and spindle are rotated in unison at a constant speed by a spindle motor.
Each disk is formed of a solid disk-shaped base or substrate, having a hole in the middle for the spindle. The substrate is commonly aluminum, although glass, ceramic, plastic or other materials are possible. The substrate is coated with a thin layer of magnetizable material, and may additionally be coated with a protective layer.
Data is recorded on the surfaces of the disks in the magnetizable layer. To do this, minute magnetized patterns representing the data are formed in the magnetizable layer. The data patterns are usually arranged in circular concentric tracks. Each track is further divided into a number of sectors. Each sector thus forms an arc, all the sectors of a track completing a circle.
A moveable actuator positions a transducer head adjacent the data on the surface to read or write data. The actuator may be likened to the tone arm of a phonograph player, and the head to the playing needle.
There is one transducer head for each disk surface containing data. The transducer head is an aerodynamically shaped block of material (usually ceramic) on which is mounted a magnetic read/write transducer. The block, or slider, flies above the surface of the disk at an extremely small distance as the disk rotates. The close proximity to the disk surface is critical in enabling the transducer to read from or write to the data patterns in the magnetizable layer. Several different transducer designs are used, and in some cases the read transducer is separate from the write transducer.
The actuator usually pivots about an axis to position the head. It typically includes a solid block near the axis having comb-like arms extending toward the disk, a set of thin suspensions attached to the arms, and an electromagnetic motor on the opposite side of the axis. The transducer heads are attached to the suspensions, one head for each suspension. The actuator motor rotates the actuator to position the head over a desired data track. Once the head is positioned over the track, the constant rotation of the disk will eventually bring the desired sector adjacent the head, and the data can then be read or written.
As computer systems have become more powerful, faster, and more reliable, there has been a corresponding increase in demand for improved storage devices. These desired improvements take several forms. It is desirable to reduce cost, to increase data capacity, to increase the speed at which the drives operate, to reduce the electrical power consumed by the drives, and to increase the resilience of the drives in the presence of mechanical shock and other disturbances.
In particular, there is a demand to reduce the physical size of disk drives. To some degree, reduction in size may serve to further some of the above goals. But at the same time, reduced size of disk drives is desirable in and of itself. Reduced size makes it practical to include magnetic disk drives in a range of portable applications, such as laptop computers, mobile pagers, and "smart cards".
An example of size reduction is the application of the PCMCIA Type II standard to disk drives. This standard was originally intended for semiconductor plug-in devices. With improvements to miniaturization technology, it will be possible to construct disk drives conforming to the PCMCIA Type II standard.
In order to shrink the size of disk drives, every component must be reduced in size as much as possible. Additionally, new designs of existing components must be developed to permit reduced size and make assembly of miniaturized components practical.
One limit on the extent to which a disk drive can be reduced in size is the disk/hub assembly. A conventional disk/hub assembly comprises a cylindrical hub having a flange at the bottom for supporting a disk stack. A motor for rotating the disks is located within the hub. The stack of disks rests on the upper surface of the flange, the hub fitting within corresponding holes of the disks. The individual disks are separated by spacer rings surrounding and adjacent to the hub. A clamping apparatus is attached to the top of the hub and applies a downward force to the disk stack, forcing the bottom disk against the flange and holding the stack in place. Where a disk drive has only a single disk, essentially the same design is used, but the clamping apparatus clamps only the one disk instead of the disk stack. The clamping apparatus is typically a flat steel ring having a formed circular ridge near its outer edge. The flat portion of the ring is attached to the upper surface of the hub with screws, while the ridge portion applies pressure to the disk stack or single disk. Several alternative clamp designs exist, but all involve multiple parts.
The conventional disk drive disk/hub design is not well suited to very small form factor disks, such as the PCMCIA Type II form factor. The hub must be sufficiently large to accommodate the screws. Even where very small screws are used, this requirement adds to the size and weight of the hub. The extremely small parts make assembly difficult. There is difficultly tolerating high mechanical shock of portable applications. The relatively thin disks tend to warp when clamped with sufficient clamping force; even a small warpage can be serious when track widths are being reduced. Finally, although the drive is much smaller, simple scaling down of the size of conventional parts will not result in any significant cost reduction; in fact, it may increase costs. It is desirable to develop an alternative hub/disk assembly which reduces costs and is more suitable to the design requirements of small form factor disk drives.